I. Technical Field
The present invention relates to the design of a linear actuator for linearly moving a transducer to a particular location on memory storage apparatus, and, more particularly, to such an actuator comprising an improved drive coil and permanent magnet arrangement.
II. Description of the Prior Art
The need for a compact, high capacity magnetic or optical disk memory storage apparatus has generated considerable interest in recent years in improving the design of such information storage apparatus. One particularly bulky element of such magnetic or optical disk memory storage apparatus in the past has been the linear actuator for moving a transducer to a particular location on magnetic or optical disk media for retrieval of information stored on the disk. One such actuator for obtaining access to two sides of a disk is disclosed in U.S. Pat. No. 4,393,425. As is disclosed in the present FIG. 1 labeled Prior Art, this linear actuator comprises a yoke 22 which forms a magnetic circuit and is shaped in the form of a letter E including thin magnetic gaps 23a and 23b. The yoke 22 is arranged such that the magnetic gaps 23a and 23b are open in the direction of a magnetic disk 24. A carriage carrying transducers pointed toward disk 24 is arranged to be slidably coupled to guide rails such that a drive coil fixed to the carriage may slide in and out of gaps 23a and 23b. Because the E-shaped yoke 22 is open at two opposite sides, the magnetic circuit obtained generates a considerable amount of leakage flux. Consequently, there is a considerable amount of intentional separation between the magnetic disk 24 and yoke 22 to protect the disk from magnetic noise generated by the magnetic circuit. As a result, the disclosed actuator is somewhat large. Furthermore, two guide rails, one fixed and one mobile, each having a circular cross section, are disclosed as being biased by a single spring imposing the mobile guide rail against the carriage carrying three sets of rollers, and against the fixed guide rail. This arrangement is somewhat mechanically unstable and requires that the transducers carried by the carriage be loosely configured when the disk 24 is disposed therebetween, so that there is a rather large gap between the transducers.
Another known linear actuator which provides an improved structure for the aforementioned linear actuator is disclosed in U.S. Pat. No. 4,414,594. As is shown in the present FIG. 2 labeled Prior Art, this linear actuator has a pair of electromagnetic motors 30 that are symmetrically disposed in a winged formation about a carriage 31 carrying stacked pairs of transducers. According to the disclosed structure, the pair of electromagnetic motors 30 provide powerful and well-balanced actuation forces permitting a relatively small compact design. Furthermore, the carriage 31 transports at least three pairs of transducers shown directed toward at least three stacked disks. Consequently, this invention permits retrieval of information from two sides of each disk of a stack of disks. Also, carriage 31 is of very compact design. Referring more particularly to the carriage 31 arrangement for guiding, there is shown a pair of guide rails 37a and 37b of circular cross section similar in design to the earlier discussed actuator design. Biasing means 39 imposes mobile guide rail 37a against pairs of rollers associated with carriage 31 and fixed guide rail 37b in a similar manner to the prior art actuator shown in FIG. 1. Consequently, there is still no improvement in permitting more compact arrangement of the three pairs of transducers mounted on the carriage 31. Also, the actuator shown in FIG. 2 comprises similar magnetic circuits 32 shaped in the form of the letter E, so that only approximately half the length of the total length of drive coils 33 may be employed for providing actuation forces.
In view of the above, there is still a requirement to further improve upon the compact design and arrangement of linear actuator such that the weight of the carriage may be reduced, the magnetic actuation force efficiency improved, the guide rail arrangement made more mechanically stable, and the transducer arrangement supported by the carriage made more compact and easily maintainable such that the transducers may be effectively and precisely positioned over stacked disks of memory storage apparatus and easily replaced.